Northeast Atlantic Stock Research Articles

Developing management plans for sprat (Sprattus sprattus) in the Celtic Sea to advance the ecosystem approach to fisheries

Sprat are commercially valuable and are an important component of the North-East Atlantic ecosystem as major predators of zooplankton, competitors with herring, and prey for piscivorous fish, marine mammals, and seabirds. Despite this, insufficient information exists for Celtic Seas sprat, one of five North-East Atlantic stocks, to estimate stock status. To ensure the sustainable exploitation of sprat, the health of the Celtic Seas ecosystem, and the wider fisheries sector, we conduct a management strategy evaluation to stress test the current single-species advice framework. The aim is to evaluate whether ecosystem objectives can be achieved under single-species maximum sustainable yield and precautionary advice frameworks. An operating model was conditioned on life history theory and strategic information from ecosystem models. We showed that in-year advice using an empirical rule could achieve management objectives and help balance the trade-offs between fishing activities and ecosystem health. The approach allows ecosystem understanding to be incorporated within existing precautionary and maximum sustainable yield frameworks to provide a robust management framework that can meet multiple objectives despite uncertainty.

The diet of juvenile Atlantic mackerel (Scomber scombrus) feeding in new northern nursery areas along the Norwegian coast

ABSTRACT The North-east Atlantic mackerel stock size increased substantially from 2006–2014 coinciding with high recruitment. This resulted in a pronounced northerly geographic expansion of mackerel, followed by an influx of juvenile mackerel into Norwegian waters. The objective of this work was to study the diet and feeding intensity of juvenile mackerel at the new nursing grounds along the Norwegian coast during the summer. Juvenile mackerel were feeding as far north as 70°N. Stomach content was analysed for the first time from co-occurring juvenile and adult mackerel at the same locations. Almost 80% of all juvenile mackerel had prey in their stomachs, and juveniles had similar stomach fullness as adult mackerel in the same areas. The juveniles preyed on a wide variety of prey species and seemed to utilize both passive filter feeding and active particulate feeding. The most abundant prey group was Appendicularia, accounting for 31% of the stomach content by weight. Juveniles fed on similar prey species as adults, but their diet niche differed somewhat as adult mackerel fed more on krill. Juvenile mackerel can thus successfully survive and feed on various prey in high latitudes and can potentially be a feeding competitor to other planktivorous fish species in the area.

Stock assessment and international mackerel fishing in the North-East Atlantic: history and modernity

In the historical aspect, the estimates of the state of the North-East Atlantic mackerel stock made at ICES in 1980–2020 are considered. The dynamics of input data for setting up models and biological reference points used in assessments in different years is analyzed. Some aspects of the international mackerel fishery are briefly presented and trends in the management of the exploitation of its stock are studied. On the basis of long-term data, the consequences of the ICES recommendations for the historical development of the international Atlantic mackerel fishery are estimated. It is shown that the significant change in trends in the dynamics of spawning stock and commercial mortality of mackerel observed in the second decade of the XXI century reflects changes in the settings of the models used and indicates the instability of estimates of mackerel stock. It is noted that only compliance with the established rules of stock operation and target biological guidelines will prevent the decline of the spawning stock of mackerel to a level below the safe biological boundaries and minimize the risk of its collapse. The necessity of strict regulation of fishing within the framework of ICES and NEAFC with the application of the principles of the “precautionary” approach and scientific research data is shown.

Highly mixed impacts of near‐future climate change on stock productivity proxies in the North East Atlantic

AbstractImpacts of climate change on ocean productivity sustaining world fisheries are predominantly negative but vary greatly among regions. We assessed how 39 fisheries resources—ranging from data‐poor to data‐rich stocks—in the North East Atlantic are most likely affected under the intermediate climate emission scenario RCP4.5 towards 2050. This region is one of the most productive waters in the world but subjected to pronounced climate change, especially in the northernmost part. In this climate impact assessment, we applied a hybrid solution combining expert opinions (scorings)—supported by an extensive literature review—with mechanistic approaches, considering stocks in three different large marine ecosystems, the North, Norwegian and Barents Seas. This approach enabled calculation of the directional effect as a function of climate exposure and sensitivity attributes (life‐history schedules), focusing on local stocks (conspecifics) across latitudes rather than the species in general. The resulting synopsis (50–82°N) contributes substantially to global assessments of major fisheries (FAO, The State of World Fisheries and Aquaculture, 2020), complementing related studies off northeast United States (35–45°N) (Hare et al., PLoS One, 2016, 11, e0146756) and Portugal (37–42°N) (Bueno‐Pardo et al., Scientific Reports, 2021, 11, 2958). Contrary to prevailing fisheries forecasts elsewhere, we found that most assessed stocks respond positively. However, the underlying, extensive environmental clines implied that North East Atlantic stocks will develop entirely different depending upon the encountered stressors: cold‐temperate stocks at the southern and Arctic stocks at the northern fringes appeared severely negatively impacted, whereas warm‐temperate stocks expanding from south were found to do well along with cold‐temperate stocks currently inhabiting below‐optimal temperatures in the northern subregion.

Horizontal and vertical movements of starry smooth-hound Mustelus asterias in the northeast Atlantic.

Commercial landings of starry smooth-hound Mustelus asterias in northern European seas are increasing, whilst our knowledge of their ecology, behaviour and population structure remains limited. M. asterias is a widely distributed demersal shark, occupying the waters of the southern North Sea and Irish Sea in the north, to at least the southern Bay of Biscay in the south, and is seasonally abundant in UK waters. There are no species-specific management measures for the northeast Atlantic stock, and the complexity of its population structure is not yet fully understood. To address this issue, we deployed both mark-recapture and electronic tags on M. asterias to gain novel insights into its horizontal and vertical movements. Our data suggest that the habitat use of M. asterias changes on a seasonal basis, with associated changes in geographical distribution, depth utilisation and experienced temperature. We report the first direct evidence of philopatry for this species, and also provide initial evidence of sex-biased dispersal and potential metapopulation-like stock structuring either side of the UK continental shelf. Investigations of finer-scale vertical movements revealed clear diel variation in vertical activity. The illustrated patterns of seasonal space-use and behaviour will provide important information to support the stock assessment process and will help inform any future management options.

Environmental change and social conflict: the northeast Atlantic mackerel dispute

A recurrent critique of the proposition of a causal relation between environmental change and social conflict is that it fails to account for the complexities and dynamics of processes of social-ecological change. In this article, we open the black box of contextual factors that influence the causal pathway from environmental change to social conflict. Firstly, we argue for the consideration of three social factors that influence that pathway: (a) institutions, (b) power, and (c) knowledge. Taking a deductive approach, we ascertain their causal importance in the case of the “mackerel dispute,” an interstate conflict that unfolded after the abrupt and rapid change in distribution of the northeast Atlantic mackerel stock after 2007. We analyze the historical development of the mackerel dispute through process tracing and demonstrate the importance and causal role of the three factors. Secondly, based on our assessment, we argue to increase the diversity of the scope conditions relevant for the environmental change-social conflict nexus. We propose to consider a wider variety of conflicts as outcome of environmental change, high-income regions as an arena for those conflicts, and a wider variety of environmental change, such as alterations in abundance in the context of climate change. Lastly, we discuss how future research on this topic can handle the wider scope conditions and greater case variability.

Can less be more? Effects of reduced frequency of surveys and stock assessments

Uncertain and inaccurate estimates are a prevailing problem in stock assessment, despite increasingly sophisticated estimation methods and substantial usage of scientific and financial resources. Annual scientific surveys and assessment group meetings require frequent use of research vessels and skilled research staff and are, therefore, particularly costly. This data- and work-intensive approach is often considered paramount for reliable stock estimates and risk management. However, it remains an open question whether the benefits of increasing assessment effort outweigh its marginal costs, or whether the potential impacts of investing less in assessments could generate net benefits. In this study, we explore how different scenarios of reduced survey and assessment frequencies affect estimated stock biomass, predicted catch, and uncertainty. Data of two Northeast Atlantic stocks, blue whiting (Micromesistius poutassou) and Norwegian spring-spawning herring (Clupea harengus), and a widely applied stock assessment model are used to compare the impacts of removing surveys and/or annual assessments. The results show that lower survey and/or assessment frequencies tend to result in deviating estimates of spawning-stock biomass and catch and larger confidence intervals, the observed differences being, however, mostly small. While scenarios without a survey datapoint in the assessment year generally produced the largest deviations in estimates, biannual surveys in general did not affect assessment performance substantially. This indicates that a reduced frequency of surveys and assessments could be an acceptable measure to reduce assessment costs and increase the efficiency of fisheries management, particularly when accompanied by thorough management strategy evaluations and risk assessments.

Thermal Niche Tracking and Future Distribution of Atlantic Mackerel Spawning in Response to Ocean Warming

North-east Atlantic mackerel spawning distribution has shifted northward in the last three decades probably in response to global sea warming. Yet, uncertainties subsist regarding on the shift rate, causalities, and how this species will respond to future conditions. Using egg surveys, we explored the influence of temperature change on mackerel’s spawning distribution (western and southern spawning components of the stock) between 1992 and 2013, and projected how it may change under future climate change scenarios. We developed three generalized additive models: (i) a spatiotemporal model to reconstruct the spawning distribution for the north-east Atlantic stock over the period 1992-2013, to estimate the rate of shift; (ii) a thermal habitat model to assess if spawning mackerel have tracked their thermal spawning-niche; and (iii) a niche-based model to project future spawning distribution under two predicted climate change scenarios. Our findings showed that mackerel spawning activity has shifted northward at a rate of 15.9 ± 0.9 km/decade between 1992 and 2013. Similarly, using the thermal habitat model, we detected a northward shift of the thermal spawning-niche. This indicates that mackerel has spawned at higher latitudes to partially tracking their thermal spawning-niche, at a rate of 28.0 ± 9.0 km/°C of sea warming. Under future scenarios (mid and end of the century), the extrapolation of the niche-based model to coupled hydroclimatic and biogeochemical models indicates that centre of gravity of mackerel spawning distribution is expected to shift westward (32 to 117 km) and northward (0.5 to 328 km), but with high variability according to scenarios and time frames. The future of the overall egg production in the area is uncertain (change from -9.3% to 12%). With the aim to allow the fishing industry to anticipate the future distribution of mackerel shoals during the spawning period, future research should focus on reducing uncertainty in projections.

The distribution of blue whiting west of the British Isles and Ireland

Northern blue whiting is a small abundant pelagic gadoid that is widely distributed in the northeast Atlantic and one of the most commercially valuable species west of the British Isles and Ireland. Over the last two decades the northeast Atlantic stock has undergone dramatic changes in abundance. The stock size decreased dramatically from 2007 to 2011, but has since shown signs of recovery. Changes in recruitment levels have occurred almost simultaneously with unusual changes in the north Atlantic ecosystem and oceanography. These links may suggest a causal linkage and the possibility of improving our understanding of the recruitment and spawning stock distribution. Here we use a set of geostatistical indices to describe the temporal and spatial patterns of the northeast Atlantic blue whiting stock in spring of 2006–2014. Geostatistical indices were computed to investigate changes in the spatial distribution, dynamics and variability of the stock in terms of density and location. Indices revealed 3 different distribution patterns over the time series. Main concentrations were either found around Rockall (first years), west of the Hebrides (2008–2013) or in the southern survey area (2014). The distribution was found to be age structured, with young blue whiting mainly concentrated in shallower areas (<1000m), along the shelf edge, and older specimens being more prominent in deeper waters (>1000m). A general additive mixed model (GAMM) was used to model the distribution of blue whiting according to environmental conditions and location.

Spatio-temporal variability in the population structure in North-east Atlantic stocks of horse mackerel (Trachurus trachurus)

Spatio-temporal variability in the population structure in North-east Atlantic stocks of horse mackerel (Trachurus trachurus)

The Alarming Decline of Mediterranean Fish Stocks

In recent years, fisheries management has succeeded in stabilizing and even improving the state of many global fisheries resources [1-5]. This is particularly evident in areas where stocks are exploited in compliance with scientific advice and strong institutional structures are in place [1, 5]. In Europe, the well-managed northeast (NE) Atlantic fish stocks have been recovering in response to decreasing fishing pressure over the past decade [3-6], albeit with a long way to go for a universal stock rebuild [3, 7]. Meanwhile, little is known about the temporal development of the European Mediterranean stocks, whose management relies on input controls that are often poorly enforced. Here, we perform a meta-analysis of 42 European Mediterranean stocks of nine species in 1990-2010, showing that exploitation rate has been steadily increasing, selectivity (proportional exploitation of juveniles) has been deteriorating, and stocks have been shrinking. We implement species-specific simulation models to quantify changes in exploitation rate and selectivity that would maximize long-term yields and halt stock depletion. We show that stocks would be more resilient to fishing and produce higher long-term yields if harvested a few years after maturation because current selectivity is far from optimal, especially for demersal stocks. The European Common Fisheries Policy that has assisted in improving the state of NE Atlantic fish stocks in the past 10 years has failed to deliver similar results for Mediterranean stocks managed under the same policy. Limiting juvenile exploitation, advancing management plans, and strengthening compliance, control, and enforcement could promote fisheries sustainability in the Mediterranean.

Brucella pinnipedialis hooded seal (Cystophora cristata) strain in the mouse model with concurrent exposure to PCB 153

Brucellosis, a worldwide zoonosis, is linked to reproductive problems in primary hosts. A high proportion of Brucella-positive hooded seals (Cystophora cristata) have been detected in the declined Northeast Atlantic stock. High concentrations of polychlorinated biphenyls (PCBs) have also been discovered in top predators in the Arctic, including the hooded seal, PCB 153 being most abundant. The aim of this study was to assess the pathogenicity of Brucella pinnipedialis hooded seal strain in the mouse model and to evaluate the outcome of Brucella spp. infection after exposure of mice to PCB 153. BALB/c mice were infected with B. pinnipedialis hooded seal strain or Brucella suis 1330, and half from each group was exposed to PCB 153 through the diet. B. pinnipedialis showed a reduced pathogenicity in the mouse model as compared to B. suis 1330. Exposure to PCB 153 affected neither the immunological parameters, nor the outcome of the infection. Altogether this indicates that it is unlikely that B. pinnipedialis contribute to the decline of hooded seals in the Northeast Atlantic.

Age-dependent prevalence of anti-Brucella antibodies in hooded seals Cystophora cristata

Investigations of hooded seals Cystophora cristata have revealed high prevalences of Brucella-positive seals in the reduced Northeast Atlantic stock, compared to the increasing Northwest Atlantic stock. This study evaluated the relation between Brucella-serostatus in seals in the Northeast Atlantic stock and age, sex, body condition and reproduction. Bacteriology documented which animals and organs were B. pinnipedialis positive. No relationship was observed between Brucella-serostatus and body condition or reproductive traits. Pups (<1 mo old) had a substantially lower probability of being seropositive (4/159, 2.5%) than yearlings (6/17, 35.3%), suggesting that exposure may occur post-weaning, during the first year of life. For seals >1 yr old, the mean probability of being seropositive decreased with age, with no seropositives older than 5 yr, indicating loss of antibody titre with either chronicity or clearance of infection. The latter explanation seems to be most likely as B. pinnipedialis has never been isolated from a hooded seal >18 mo old, which is consistent with findings in this study; B. pinnipedialis was isolated from the retropharyngeal lymph node in 1 seropositive yearling (1/21, 5%). We hypothesize that this serological and bacteriological pattern is due to environmental exposure to B. pinnipedialis early in life, with a subsequent clearance of infection. This raises the question of a reservoir of B. pinnipedialis in the hooded seal food web.

Entry and Elimination of Marine Mammal Brucella spp. by Hooded Seal (Cystophora cristata) Alveolar Macrophages In Vitro

A high prevalence of Brucella pinnipedialis serology and bacteriology positive animals has been found in the Northeast Atlantic stock of hooded seal ( Cystophora cristata ); however no associated gross pathological changes have been identified. Marine mammal brucellae have previously displayed different infection patterns in human and murine macrophages. To investigate if marine mammal Brucella spp. are able to invade and multiply in cells originating from a presumed host species, we infected alveolar macrophages from hooded seal with a B . pinnipedialis hooded seal isolate. Hooded seal alveolar macrophages were also challenged with B . pinnipedialis reference strain (NCTC 12890) from harbor seal ( Phoca vitulina ), B . ceti reference strain (NCTC 12891) from harbor porpoise ( Phocoena phocoena ) and a B . ceti Atlantic white-sided dolphin ( Lagenorhynchus acutus ) isolate (M83/07/1), to evaluate possible species-specific differences. Brucella suis 1330 was included as a positive control. Alveolar macrophages were obtained by post mortem bronchoalveolar lavage of euthanized hooded seals. Phenotyping of cells in the lavage fluid was executed by flow cytometry using the surface markers CD14 and CD18. Cultured lavage cells were identified as alveolar macrophages based on morphology, expression of surface markers and phagocytic ability. Alveolar macrophages were challenged with Brucella spp. in a gentamicin protection assay. Following infection, cell lysates from different time points were plated and evaluated quantitatively for colony forming units. Intracellular presence of B . pinnipedialis hooded seal isolate was verified by immunocytochemistry. Our results show that the marine mammal brucellae were able to enter hooded seal alveolar macrophages; however, they did not multiply intracellularly and were eliminated within 48 hours, to the contrary of B. suis that showed the classical pattern of a pathogenic strain. In conclusion, none of the four marine mammal strains tested were able to establish a persistent infection in primary alveolar macrophages from hooded seal.

Use of saggital otolith shape analysis to discriminate Northeast Atlantic and Western Mediterranean stocks of Atlantic saury, Scomberesox saurus saurus (Walbaum)

The aim of this study was to test the hypothesis that Atlantic saury stocks from the Mediterranean Sea and northeastern Atlantic could be identified by means of saggital otolith shape. Saury is a pelagic fish inhabiting the north Atlantic that undertakes long migrations for feeding and reproduction. A combination of otolith shape indices and elliptic Fourier descriptors are analysed by multivariate statistical procedures. The results obtained show that saury from the Mediterranean Sea and northeastern Atlantic can be distinguished using otolith shape analysis. Whether or not those differences are due to genetic isolation is not tested here but possible drivers of the observed shape variation are explored.

Age-structure-dependent recruitment: a meta-analysis applied to Northeast Atlantic fish stocks

Abstract Brunel, T. 2010. Age-structure-dependent recruitment: a meta-analysis applied to Northeast Atlantic fish stocks. – ICES Journal of Marine Science, 67: 1921–1930. Exploitation alters the age structure of fish stocks. Several stock-specific studies have suggested that changes in the age structure might have consequences for subsequent recruitment, but the evidence is not universal. To investigate how common such effects are among 39 Northeast Atlantic fish stocks, relationships were tested between age structure (spawner mean age, age diversity, and proportion of recruit spawners) and recruitment (number of recruits, sensitivity to environment, and recruitment variability). Significant correlations in the expected direction were observed for a few stocks, but not for the majority; significant correlations in the opposite direction were also found. Meta-analyses combining the stock-level tests revealed that none of the effects were significant overall. However, effects were significant for some species (cod, haddock, and plaice) and indices. The low variability in the age structure might explain the absence of significant effects for individual stocks. Other reasons could be the absence of a biological basis (reproductive characteristics not dependent on age) or the stronger influence of environmental variability than of age structure on recruitment.

Investment in maturity-at-age and -length in northeast Atlantic cod stocks

The maturation schedule (maturity ogives) for populations differs with geographic location, and cod ( Gadus morhua) stocks are no exception. The environment (latitudinal effects) will have an impact on the maturation schedule, with northern (colder water) stocks growing more slowly and maturing at a greater age. This is, however, modified by the impacts of fishing, whereby under severe exploitation, maturation tends towards an earlier age. Cod in the Irish Sea are towards the southern end of the species’ range and the stock is severely depleted, with most males and females maturing between 2 and 3 years of age and at a relatively small size. The North Sea cod stock is considered to be harvested unsustainably, and, in addition, in recent years has shown the classic shift in maturity schedule to most fish maturing at a younger age and smaller size. The Barents Sea (Northeast Arctic) cod stock has undergone major changes in population size, but is currently not overexploited. There have also been shifts in the maturation schedules of Northeast Arctic cod. However, over the past decade or so, there has not been a clear trend in the age- or length-at-50% maturity with time or population size. The relationship between the age- and length-at-50% maturity differs markedly between the three cod stocks (Irish, North and Barents Seas), when considered over years and by year classes, which suggests that there may be stock- or area-specific characteristics. Such stock-specific differences will have consequences for applying relationships between areas where the maturity schedules are dynamic, e.g. through climate change or under severe or changing exploitation patterns.

Metazoan gill parasites of wild albacore Thunnus alalunga (Bonaterre, 1788) from the Balearic Sea (western Mediterranean) and their use as biological tags

Metazoan gill parasites of 30 albacore Thunnus alalunga caught in the Balearic Sea (western Mediterranean) were examined for parasites with the aim to evaluate their possible use as biological tags. A total of 9 species of parasites were found: 1 capsalid monogenean, 6 didymozoid trematodes and 2 crustaceans. Most of the parasites collected were didymozoids (95.8% of all specimens) and Didymozoon longicolle was the dominant species. Albacore is a new host record for Capsala paucispinosa and Didymozoon pretiosus, while Didymosulcus aahi, Didymosulcus dimidiatus, Nematobothrium latum and Rocinela sp. are for the first time reported from the Mediterranean Sea. Significant differences were found grouping data by host size, with lower infection levels in the larger sized fish, whereas no differences were found between host sex. Most of the parasites showed a high site selection: D. aahi, D. dimidiatus and D. longicolle had significant differences of prevalence between internal and external margins of gill filaments, and almost all specimens of Pseudocycnus appendiculatus were attached to the gill filaments of the second and third holobranchs. The usefulness of parasites as biological tags is discussed; particularly, D. longicolle and D. pretiosus could be used to separate Mediterranean and northeast Atlantic stocks of albacore.

Minimum landing size for Northeast Atlantic stocks of deep-water red crab, Chaceon affinis (Milne Edwards and Bouvier, 1894)

Abstract Robinson, M. 2008. Minimum landing size for Northeast Atlantic stocks of deep-water red crab, Chaceon affinis (Milne Edwards and Bouvier, 1894). – ICES Journal of Marine Science, 65: 148–154. Annual landings of the deep-water red crab (Chaceon affinis) in the NE Atlantic have fluctuated around 1000 t for much of the past decade, but they dropped significantly in 2006. No EU or National Member State legislation governs the harvest of the species, and because of the on-board processing, it is difficult to set a single minimum landing size (MLS) based on carapace width (CW) alone. As the claws are detached during processing and represent the most valuable component of the catch, a supplementary MLS based on claw length (CL) for onshore inspection and enforcement would seem appropriate. Physiological size-at-maturity and morphometric claw data were used to derive primary (CW) and secondary (CL) MLS. All males and females are mature at 110 and 125 mm CW, respectively, and 50% of females are mature at 109 mm CW. Because of a lack of information relating to the biology, distribution, and fishing mortality of the species, and a doubt as to real landing statistics, a conservative MLS of 120 mm CW and 72 mm CL is suggested, representing the first use of commercial fisheries data to suggest MLS for this otherwise unregulated fishery.

Using isoelectric focusing to discern enzyme variation in northeast Atlantic stocks of the harp seal (Phoca groenlandica).

Liver and/or muscle samples were collected from harp seals on the breeding and moulting grounds in the White Sea area (N = 316) and in the Greenland Sea (N = 225). Of a total of 25 presumptive loci detected by isoelectric focusing on polyacrylamide gels (IFPAG), 11 were variable. Of these, 4 were polymorphic at the 95% level, another 2 at the 99% level. The study shows that the higher resolving capacity obtained by IFPAG, as compared to starch gel electrophoresis, increases the number of electrophoretically detectable polymorphic loci in this species. The paper also compiles a set of methodical modifications which adapt IFPAG to large scale multilocus screening. The study indicates no marked differences between the White Sea and Greenland Sea stocks in frequency distributions of the consistently resolved enzyme systems. Other evidence suggests that potential exchange of genetic material between Northeast Atlantic harp seal stocks may still be so limited that for management purposes the stocks may be regarded as separate and self-sustaining units.